The number of smart phones, wireless-enabled tablets and laptop computers in the Universal Mobile Telecommunications System (UMTS) networks is growing rapidly. It is important for network operators to evolve their networks in terms of capacity and coverage so that positive user experience can be sustained.
Deployment of low-power nodes (LPNs) is seen as a powerful tool to achieve the goal. A network consisting of traditional macro NodeBs and LPNs is referred to as a heterogeneous network. Two use-cases for heterogeneous network deployment that may be envisioned are coverage holes and localized traffic hotspots. Deployment of LPNs as a complement to a macro network then aims at improving coverage and capacity, respectively.
In the heterogeneous network deployment, an LPN can either form a separate cell (such as, a pico cell or a micro cell) by itself or be one of the spatially separated TRPs in one logical cell. The former case is referred to as separated-cell scenario, while the latter case is referred to as combined-cell (or shared-cell) scenario.
As compared with the separated-cell scenario, signalling reception and interference handling for the combined-cell scenario are much easier. Moreover, for the combined-cell scenario, no handover is needed between the different TRPs in the same combined cell, ensuring a more smooth mobility procedure and easing the Radio Network Controller (RNC) load.
However, according to the prior-art transmission scheme for the combined-cell scenario, all TRPs within a combined-cell transmit the same physical channel. This adversely limits the system capacity of the combined cell.
At Technical Specification Group-Radio Access Network (TSG-RAN) meeting #56, a study item (SI) was initiated on Universal Mobile Telecommunications System (UMTS) Heterogeneous Networks for 3rd Partnership Project (3GPP) Rel-12 [1]. There exist more opportunities for 3GPP Rel-12 to include value-added features to further improving the performance of Heterogeneous Networks.